1. Technical Field
The present invention is directed to apparatus and methods for gaining percutaneous access to body anatomy, for example an organ or a body lumen.
2. Background of the Invention
Many medical procedures require the percutaneous placement of an interventional medical device, such as a catheter, into a body lumen such as an artery or vein. Such interventional devices may be used for, among other things, blood pressure monitoring, blood sampling, and the administration of fluids and medicaments to a patient.
Typically, such devices are introduced into the vascular system using the well-known Seldinger percutaneous entry technique. In the Seldinger technique, the physician makes an entry into the artery or vein with a beveled needle. A wire guide is passed through the bore of the needle into the artery or vein. The needle is thereafter withdrawn, leaving the wire guide in place. The catheter or other interventional device is then passed over the wire guide, through the puncture, and into the artery or vein at the needle puncture site. Once the catheter is in place, the wire guide can be withdrawn.
One of the disadvantages of this procedure is that the initial needle stick must normally be made with a needle that is large enough to accept the wire guide. Conventional wire guides often comprise a tightly wound helical stainless steel wire coil. In order to have sufficient rigidity to properly support and lead many standard catheters and other interventional devices in common use in modern medicine, such wire guides are typically constructed to have an outer diameter in a range on the order of 0.035 to 0.038 inch (0.89 or 0.97 mm). This diameter of wire guide will typically pass through an 18 gauge thin wall needle. An 18 gauge needle typically has a 0.050 inch (1.27 mm) outer diameter (O.D.) and a 0.042 inch (1.07 mm) inner diameter (I.D.).
The 18 gauge needle is the most common sized needle used for initial vascular access, and has become a standard needle for use with the Seldinger technique for percutaneous catheterization. However, the O.D. of an 18 gauge needle is just large enough to damage tissue or cause excessive bleeding if it does not enter the vessel correctly, or if it inadvertently penetrates an organ or other unintended body structure. As a result, it is desirable to utilize a smaller gauge needle, such as a 21 gauge thin wall needle, for initial entry. A 21 gauge thin wall needle typically has a 0.032 inch (0.81 mm) O.D. and a 0.022 inch (0.56 mm) I.D., or smaller. Needles of 21 gauge thin wall, or smaller, are considered small enough that they do not damage tissue or organs, or cause excessive bleeding if inserted off target. In addition, smaller gauge needles generally have correspondingly shorter bevels at the needle tip compared to the size of the bevel tip of an 18 gauge needle. Thus, it is much easier to get a short bevel into the lumen of a small vessel than the longer bevel of the 18 gauge needle.
Unfortunately, the bore of a needle of 21 gauge, or smaller, is not large enough to enable a standard 0.035 inch or 0.038 inch (0.89 mm or 0.97 mm) diameter wire guide to be passed therethrough. The largest wire guide that can be easily introduced into such small gauge needles is normally a wire of 0.018 inch (0.46 mm) O.D. However, many diagnostic and interventional devices need at least a 0.035 inch (0.89 mm), and more preferably a 0.038 inch (0.97 mm), diameter wire guide to provide sufficient support to enable the physician to optimally introduce and manipulate the device through the vasculature over the wire. Thus, unless a larger diameter wire guide is introduced into the vasculature, many such devices cannot be successfully introduced.
U.S. Pat. No. 4,650,472 describes an apparatus which enables a physician to introduce a medical device, such as a catheter, into the body of a patient by making the initial puncture with a small gauge needle, such as a 22 gauge (0.028 inch; 0.72 mm O.D.) needle, in place of the larger conventional 18 gauge needle. The '472 patent is incorporated by reference herein. A 0.018 inch (0.46 mm) outer diameter wire guide is initially inserted through the bore of the small gauge (e. g. 22 gauge) needle. The needle is thereafter withdrawn, and a removable inner cannula, or dilator, is provided over the wire guide but inside an outer sleeve portion of the catheterization apparatus. This removable inner cannula has a tapered tip, and provides a transition between the large distal opening of the outer sleeve and the 0.018 inch wire guide. The inner cannula is generally on the order of 0.038 inch (0.97 mm) O.D., and the outer sleeve is sized to fit over the inner cannula.
The outer sleeve and the inner cannula of the apparatus disclosed in the '472 patent are normally inserted into the blood vessel in tandem. The diametrical transition of the leading end of this tandem is intended to minimize the trauma that may otherwise be caused by the insertion of a large diameter outer sleeve over a small diameter wire guide. Once the outer sleeve is properly positioned within the blood vessel, the inner cannula and the smaller wire guide can be withdrawn, leaving the outer sleeve in place. A larger diameter (0.035 to 0.038 inch) (0.89 to 0.97 mm) wire guide can then be introduced through the outer sleeve and into the vessel.
In summary, the '472 patent device is used according to the following steps:                1. Initial needle stick with a 22 gauge needle.        2. Insert a 0.018 inch diameter wire guide through needle.        3. Remove the needle leaving the 0.018 inch diameter wire guide in place.        4. Insert the outer sleeve and the inner cannula in tandem.        5. Remove the inner cannula and 0.018 inch diameter wire guide leaving the outer sleeve in place.        6. Insert a larger 0.035-0.038 inch diameter wire guide through the outer sleeve.        
If desired, the outer sleeve can thereafter be removed from the patient, leaving the larger wire guide in the vessel ready to accept a catheter or other interventional device. The apparatus of the '472 patent has been successfully used to percutaneously insert a medical device, such as a catheter, having a large diameter O.D. into a blood vessel when the initial insertion is made with an introducer needle and a wire guide which are much smaller in diameter than the distal opening of the catheter.
Other medical devices are used for percutaneous access to organs or other anatomy within a body for procedures such as interventional radiology One such device is the “Neff Percutaneous Access Set” available from Cook Incorporated, catalogue number prefix NPAS. The set has an access needle, a wire guide, a stiffening cannula, an introducer (functionally a dilator), and a sheath (functionally a catheter or outer sleeve). The first step in using the set is to penetrate the skin and body with the access needle and place the tip of the access needle at a desired location. The wire guide is then inserted through the access needle. Next, the access needle is removed leaving the wire guide in place. The introducer is inserted into the sheath and the stiffening cannula is inserted into the introducer. The assembly is then inserted into the body over the wire guide. Finally, the wire guide, introducer and stiffening cannula are removed, leaving the sheath in place.
In summary, the Neff device is used according to the following steps:                1. Initial needle stick and placement of the access needle.        2. Insert the wire guide through the access needle.        3. Remove the access needle leaving the wire guide in place.        4. Insert the sheath/introducer/stiffening cannula assembly over the wire guide.        5. Remove the introducer/stiffening cannula leaving the sheath in place.        
Apparatus and methods for gaining percutaneous access to body anatomy having fewer components and fewer steps are generally desired.